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200                                          HORNS                                         CHAI
the likenesses which Titanotherium shows to the Artiodactyl*
must be either purely superficial and secondary, or a cropping
out of ancient characters which had been dormant for man^
Horns.—The Ungulata are the only order of mammals whicl
possess horns; as they are on the whole a more defenceless grou|
than the Carnivora, it may be that the horns are a counterpoise
to the teeth and claws of the latter; need for defence and foi
armature in the combats with their own kind for the favours
of the does has led to a different kind of protective and
aggressive mechanism. Horns as weapons are, however, parti-
cularly effective in this group wherever they exist. A Huminant
is most frequently a large and heavy animal without the agility
and litheness of the Carnivore. It is precisely to this sort oi
animal, where weight is an important consideration, that horns are
the most suitable weapons. This is further shown by the fact
that although the general term horn is used to describe the
weapons of the Ungulate mammals, there is more than one kind
of structure included under this general term; it is indeed prob-
able that the extreme terms in the series of horns have been
independently acquired by their possessors. There is but little
in common between the horns of a Giraffe and of a [Rhinoceros.
In the .Rhinoceros we have one or two horns, in the latter
case one placed behind the other, which are purely epidermic
growths; they may indeed be regarded as matted masses of hair,
borne, it is true, upon a boss of bone, which however is not
a separate structure. The Giraffe supplies us with the simplest
term in that series of horns which are partly epidermal and partly
bony. The paired horns of this animal have often been contrasted
with those of the Deer, for example; but there is no fundamental
difference between them. In the Giraffe a pair of bony out-
growths, originally separate from the skull which bears them, but
ultimately ankylosed to it, are covered by a layer of entirely un-
modified skin. A distinction of undoubtedly practical importance
is usually drawn between the Hollow-horned Buminants, i.e. Oxen,
G-oats and Antelopes, and the Deer tribe. There is nevertheless
no fundamental distinction. In the Antelopes there is a core of
bone, the " os cornu" as it has been termed, which is covered
by a horny layer, the horn proper, variously modified in shape and
size according to the genus or species. In the Deer there is the